This invention relates generally to data communciation systems and addressing apparatus therefore, and more particularly to address assignment and recognition apparatus for use in large numbers of terminal devices found in such systems.
In various types of data communication and control systems, some type of message generator, such as a computer, is provided to transmit messages containing command and address data to remotely located terminal units. In order for a terminal unit to react to command functions specified by a message, that unit must first recognize the message address.
The terminal units used in the types of communication systems being considered generally contain some type of address recognition logic or circuitry designed to recognize a specific address. The recognizing of an address by this logic effectuates the generation of an enable signal which directs the recognizing terminal unit to carry out its designed function or functions as specified by the command portion of the received message.
In some types of communication systems, it is desirable to be able to selectively address large numbers of remote terminal units. Typical of these systems are automatic remote meter reading and control systems used for collecting meter data from consumer residences and controlling loads at those residences. In these types of systems, messages or commands and data are transferred between a message generator and the remote terminals over various types of communication links, such as telephone lines, power lines, or combinations thereof.
Typical systems of the preceding type are described in U.S. Pat. Nos. 3,942,170, Distribution Network Powerline Carrier Communication System; 3,702,460, Communication System for Electric Power Utility; 3,656,112, Utility Meter Remote Automatic Reading System; 3,924,224, Meter Reading System; and, 3,900,842, Remote Automatic Meter Reading and Control System.
Meter reading and control systems of the preceding type frequently have many terminal units connected to a single power line. A message generator transmits messages to these terminal units over the power line whereby each of the units simultaneously receives each transmitted message. In order for the terminal units to respond to the messages, they must each be able to recognize their own address. To address all of the terminal units on a single power line, a separate message must be transmitted for each terminal unit. Thus, it can be seen, when the quantity of terminal units on a power line numbers in the thousands, a considerable amount of addressing time is used, even with a high speed computer serving as the message generator.
While the individual addressing of terminal units is a desirable feature, and frequently essential, in the preceding types of systems, cost savings in equipment and message and data transmittal times can be realized by providing addressing means in each terminal unit which not only allows individual addressing, but extends the addressing capabilities of the system to the simultaneous addressing of all units in the system, as well as the simultaneous addressing of groups and sets of terminal units. A representative type of system which provides this extended addressing capability and which makes use of the present invention, is disclosed in U.S. Patent application Ser. No. 653,859, filed Jan. 30, 1976 entitled Automatic Remote Meter Reading and Control System, and assigned to the assignee of the present invention.
Thus, it can be seen that a need exists for improved apparatus for use in each of a plurality of terminal units or user devices which overcomes the shortcomings of the prior art by extending the addressing capabilities to many combinations of large quantities of such units when implemented into a system.